Conventionally, it has been well known that: there is a material, emitting visible or substantially visible light at a low temperature such as a room temperature by receiving external stimulation, which functions as a so-called fluorescent phenomenon. Materials bringing about such a fluorescent phenomenon, namely fluorescent materials, are used in a panel light such as a fluorescent lamp and in a display such as a so-called Braun tube of CRT (Cathode Ray Tube).
It is typical that ultraviolet ray irradiation, electron ray irradiation, X-ray irradiation, radioactive ray irradiation, application of an electric field, chemical reaction, and the like are performed as external stimulation bringing about the fluorescent phenomenon, but a material that emits light by receiving mechanical force from outside is not well known.
The present inventors proposed the following two light-emitting materials. The one is a high intensity mechanoluminescence material (Japanese Unexamined Patent Publication No. 49251/2001 (Tokukai 2001-49251)(Publication date: Feb. 20, 2001)) made of (a) a material, constituted of at least one kind of aluminate having non-stoicheiometric composition, that includes lattice defect in which light is emitted when carriers excited by mechanical energy are restored to a normal state, or (b) a material whose mother body material includes at least one kind of a metal ion selected from a rare earth metal ion and a transition metal ion as a central ion of a luminescence center. The other is a light-emitting material (Japanese Unexamined Patent Publication No. 313878/2000 (Tokukai 2000-313878)(Publication date: Nov. 14, 2000)) whose mother body material is constituted of Y2SiO5, Ba3MgSi2O8, and BaSi2O5. However, these light-emitting materials are so insufficient in the luminous intensity that they cannot be put into practical usage. Thus, a material whose luminous intensity is higher has been required.